Jet for Use in a Jet Mill Micronizer

ABSTRACT

The current invention provides an improved jet nozzle suitable for use in a micronizing jet mill or retrofitting to an existing jet mill. The improved jet nozzle incorporates a coanda effect inducing element to enhance entrainment of particles to be ground within the vortex created by the micronizing jet mill. When the jet mill uses steam to generate the jet, use of the improved nozzle will reduce energy costs by increasing the efficiency of the jet mill.

BACKGROUND OF THE INVENTION

Jet mill micronizers are commonly used to reduce the particle size offriable material to the micron range. Typical jet mill micronizers feedthe friable material into a vortex created by injection of a fluid suchas compressed air, gas or steam through a nozzle into the micronizer.The vortex entrains the friable material and accelerates it to a highspeed. Subsequent particle on particle impacts within the micronizercreate increasingly smaller particles, with particles of the desiredsize ultimately moving to the center of the micronizer where they exitthrough a vortex finder.

The efficiency of the micronizer is dictated by the ability to properlyentrain the friable material within the jet stream created by theinjected gas. Over the years, the industry has attempted to improve theentrainment of the particles through changes in nozzle design as well asthrough recirculation devices incorporated into the micronizer. Whilesuch efforts have met with limited success, they frequently rely uponcomplicated designs subject to wear and increased maintenance.

One attempt to improve the efficiency of a micronizer resulted in thedevelopment and use of the now standard convergent-divergent nozzles.Converging-diverging nozzles generate extremely high velocity gaseousstreams commonly achieving supersonic velocities. However, because thegaseous streams expand within the nozzle, entrainment of particleswithin the resulting jet is difficult. Thus, the benefits of thesupersonic velocity are not generally imparted to the friable material.

High pressure steam is commonly used to generate the micronizing jetwhen milling titanium dioxide particles to pigmentary size. In view ofthe energy costs associated with steam generation, improved entrainmentefficiencies can lead to significant cost savings during the TiO₂pigment manufacturing process. The quantity of steam used during theTiO₂ micronization process, for example, is typically quite substantial,generally varying between about 0.5 to greater than two tons per ton ofpigment.

In view of the significant energy costs associated with steam jet mills,it would be desirable to provide an improved jet nozzle which enhancesentrainment of particles to be milled. Preferably, such improvementswould be provided without significant design changes to the micronizer.Further, it would be even more beneficial if the changes enabling theimproved operations of the micronizer could be readily retrofitted toexisting units. The current invention, as described herein, provides foreach of the above needs through an improved micronizer jet nozzle.

SUMMARY OF THE INVENTION

The current invention provides an improved jet nozzle for use in amicronizing jet mill. The nozzle of the current invention includes anozzle body having a passageway extending from a first open end to asecond open end suitable for forming a gaseous jet. Located within thepassageway is a coanda effect inducing element. Preferably, the coandaeffect inducing element extends outwardly from the exit (second end) ofthe passageway.

In another embodiment, the current invention provides an improved jetnozzle for use in a micronizing jet mill. The jet nozzle has a nozzlebody with a conduit passing through the length of the nozzle bodyproviding a passageway for generating a gaseous jet. The exit point ofthe nozzle forming the gaseous jet preferably has a slot-like design.Positioned within the passageway and preferably extending outwards fromthe exit point of the passageway is a coanda effect inducing element.Preferably, the coanda effect inducing element has a configurationcorresponding to the slot-like exit of the passageway. Thus, theslot-like exit of the passageway and the coanda effect inducing elementdefine a generally consistent gap suitable for generating the steam jet.

Still further, the current invention provides an improved jet nozzle foruse in a micronizing jet mill. The improved nozzle comprises a nozzlebody with a passageway passing the length of the nozzle body forgenerating a gaseous jet. The exit point of the nozzle has a slot-likedesign defined by two longer, essentially inwardly hyperbolic sides andtwo opposing generally rounded ends. Removably positioned within thepassageway and preferably extending outwards from the exit point of thepassageway is a coanda effect inducing element. Preferably, theremovable coanda effect inducing element has a configurationcorresponding to the slot-like exit of the passageway. Thus, theslot-like exit of the passageway and the coanda effect inducing elementdefine a generally consistent gap through which the gaseous steam flowsto form the jet. While other means may be employed to secure the coandaeffect inducing element in position within the nozzle, the preferredembodiment utilizes a hollow set screw having a passageway running thelength of the screw. The screw is inserted into the first end of the jetnozzle following placement of the coanda effect inducing element withinthe nozzle, thereby securing the coanda effect inducing element inposition within the nozzle.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 depicts a typical micronizing jet mill.

FIG. 2 is a perspective view of a preferred embodiment of an improvedjet nozzle, including the coanda effect inducing element positionedwithin the jet nozzle.

FIG. 3 is an exploded view of the improved jet nozzle of FIG. 2.

FIG. 4 depicts the extension of the coanda effect beyond the exit pointof the jet nozzle and represents the speed of the gaseous jet.

FIG. 5 depicts the deflection of particles around the gaseous jet whenusing a prior art nozzle.

FIG. 6 depicts the improved entrainment of particles when using the jetnozzle of the current invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In 1910, Henri Coanda first observed a phenomenon wherein a free jetemerging from a nozzle attached itself to a nearby surface. Known as thecoanda effect, this phenomenon is the result of low pressure developingbetween the free flowing stream of gas and the wall. The coanda effectcan be observed in both liquid and gaseous fluids.

The current invention takes advantage of the coanda effect to extend athin layer supersonic zone 31 outward from the jet nozzle 10. Asdepicted in FIG. 4, the current invention extends supersonic zone 31 atleast one inch outward from the exit point 26 of the nozzle 10. Whenused in a titanium dioxide micronizing process, the current inventionprovides an effective grinding zone equal to currently available fullcone jet nozzles. The nozzle of the current invention provides thisequivalent grinding zone while reducing the steam requirements by half.Thus, the current invention satisfies the above indicated needs of theindustry.

Preferred embodiments of the current invention will be described withreference to FIGS. 1-3 and in particular with reference to FIGS. 2 and3. FIG. 1 depicts a typical micronizer jet mill 5 which may beretrofitted with improved jet nozzle 10 of the current invention.

Improved jet nozzle 10 of the current invention is depicted in detail inFIGS. 2 and 3. With reference of FIG. 3, nozzle 10 includes a nozzlebody 14 having a passageway 18 therethrough. Passageway 18 has a firstopen end 22 and second open end 26 also referred to herein as the exitpoint 26 or jet forming exit 26. Located within passageway 18 andpreferably extending outward from exit point 26 is a coanda effectinducing element 30. Coanda effect inducing element 30 extends outwardsfrom exit point 26 a distance sufficient to ensure development of thecoanda effect. Typically, this distance is between about 2.5 mm (0.1inch) and about 38.1 mm (1.5 inches).

As depicted in FIG. 2, coanda effect inducing element 30 preferably hasa configuration which conforms to the configuration of exit point 26.Finally, in a preferred embodiment, coanda effect inducing element 30 ispreferably removably secured within passageway 18 by a retainer such asa set screw 34. Set screw 34 also has a conduit or passageway 38extending through screw 34. Thus, when installed within micronizer 5,compressed gas or steam at a pressure suitable for forming the desiredjet initially enters nozzle 10 by passing through screw 34 into nozzlebody 14 and exiting at exit point 26. As mentioned above, other optionsare available for removably securing the element 30 in position withinpassageway 18, including using a snap ring attachment, an indexedfriction fit or even a tack weld of the element 30 within the passageway18.

As the steam jet exits nozzle body 14, it will be attracted to andmaintained in close proximity to coanda effect inducing element 30 bythe coanda effect. Due to the induced coanda effect, the resulting jet'ssupersonic zone 31 will be extended outward from nozzle 10 a greaterdistance than would be true of a jet under the same pressure andtemperature conditions, without using coanda effect inducing element 30.

As shown in FIG. 4, supersonic zone 31 is extended at least one inchbeyond exit point 26. FIG. 4 further provides a depiction of the speedof the resulting jet in gray scale. As shown, even the lower edge 39 ofsupersonic zone 31 retains a significant jet velocity. Typically, jetvelocity at the lower edge 39 of supersonic zone 31 will be about Mach1.8 to about Mach 1.9. In contrast, prior art devices lacking a coandaeffect inducing element 30 would experience rapid dissipation of the jetin the region adjacent to nozzle 10. In general, jet velocities in thecorresponding regions without use of element 30 would normally be aboutMach 1, and require approximately 2× as much steam to attain a zone ofless than equivalent length. The improved velocities throughoutsupersonic zone 31 produce enhanced entrainment of particles within jetregion 35.

The improved entrainment of particles within supersonic zone 31 isevident from a comparison of FIG. 5 to FIG. 6. FIGS. 5 and 6 depict theinfluence of jet region 35 on representative particle tracking lines 33and 37. In FIG. 6, the particle tracking lines 33 indicate that fourrepresentative particle tracks 37 are drawn into supersonic zone 31while only two particle tracks 33 do not enter supersonic zone 31. Incontrast, FIG. 5 depicts operating the jet without coanda effectinducing element 30. As shown in FIG. 5, four particle tracks 33 do notenter jet region 35, with only two particle tracks 37 being entrained byjet region 35. Thus, use of coanda effect inducing element 30 withinnozzle 10, as depicted in FIGS. 4 and 6, increases the efficiency ofsupersonic zone 31, thereby enabling a corresponding reduction in steamusage for a desired degree of grinding.

In the preferred embodiment, exit point 26 preferably has a modifiedslot-like configuration wherein opposing walls 44 and 46 are pinchedinwards toward one another, each presenting a generally inwardlyhyperbolic shape, with the opposing shorter ends 48 and 50 beinggenerally rounded in configuration. To obtain maximum efficiency ofnozzle 10, coanda effect inducing element 30 preferably has aconfiguration which conforms to the configuration of exit point 26.Typically, the conforming configuration extends from exit point 26 intopassageway 18 a distance of about ten times (10×) to about twenty times(20×) the width of the air passage or gap 52 defined between the outersurface of coanda effect inducing element 30 and the inner surface ofexit point 26. Thus, if gap 52 is about 0.254 mm (about 0.01″) wide,then the conforming configuration will extend about 2.54 mm to about10.16 mm (about 0.1″ to about 0.2″) into passageway 18. Alternatively,the conforming configuration may characterize the entire length ofcoanda effect inducing element 30 from end 36 to flange 54 or someintermediate distance.

In alternative embodiments, exit point 26 may have a differentconfiguration than depicted in FIGS. 1 and 2. For example, exit point 26may have a conventional slot like opening wherein sidewalls 44, 46 areessentially parallel with rounded or squared ends 48, 50. Preferably,coanda effect inducing element 30 used in conjunction with exit point 26will have a corresponding configuration. However, the current inventioncontemplates the use of coanda effect inducing element 30 having aconfiguration which does not conform to the configuration of exit point26. For example, coanda effect inducing element 30 may have an oval,elliptic or any other curved surface suitable for inducing a coandaeffect on the steam exiting the nozzle body 14 while exit point 26 maybe a standard slot opening or other configuration including but notlimited to oval, circular, multi-slotted and multi-lobed.

In a preferred embodiment, coanda effect inducing element 30 carries aflange 54 suitable for retaining coanda effect inducing element 30within passageway 18 by engaging a lip or other similar device (notshown). Following positioning of coanda effect inducing element 30within passageway 18, set screw 34 is threaded into nozzle body 14.Although shown as having a fixed position within nozzle body 14, coandaeffect inducing element 30 may be adjustably secured within passageway18 thereby allowing fine tuning of micronizer 5 for changes in operatingconditions. Methods for adjustably securing coanda effect inducingelement 30 within passageway 18 are well known to those skilled in theart and will typically use a solenoid or stepper motor operating in amanner similar to an idle air control valve commonly found a modem fuelinjected engine.

In addition to the benefits depicted by FIG. 6, the current inventionalso provides a thicker supersonic zone. Thus, the current inventionfurther improves entrainment of particles by extending the supersonicjet further into the layer of particles entering micronizer 5.Additionally, stabilization of the supersonic zone by use of the currentinvention enhances back flow of particles into the resulting jet.

While preferred embodiments of the present invention have beenillustrated for the purpose of the present disclosure, other embodimentsof the current invention will be apparent to those skilled in the artfrom a consideration of this specification, the drawings or practice ofthe invention disclosed herein. Thus, the foregoing disclosure willenable the construction of a wide variety of apparatus within the scopeof the following claims. Accordingly, the foregoing specification isconsidered merely exemplary of the current invention with the true scopeand spirit of the invention being indicated by the following claims.

1. A jet nozzle for use in a micronizing jet mill comprising: a nozzlebody having a first open end and a second open end with a passagewayjoining said first and second ends; a coanda effect inducing elementpositioned within said passageway and extending outward from said secondend of said nozzle.
 2. A jet nozzle for use in a micronizing jet millcomprising: a nozzle body having a first open end and a second open endwith a passageway joining said first and second ends; a coanda effectinducing element positioned within said passageway and extending outwardfrom said second open end of said nozzle wherein said coanda effectinducing element has a geometric configuration corresponding to thegeometric configuration of said second open end of said nozzle.
 3. A jetnozzle for use in a micronizing jet mill comprising: a nozzle bodyhaving a first open end and a second open end, said first and secondends being joined by a passageway passing through said nozzle, whereinsaid second open end has a slot-like configuration; a coanda effectinducing element positioned within said passageway, said coanda effectinducing element extending outward from said nozzle through said secondend, wherein said coanda effect inducing element has a configurationsubstantially similar to the slot-like configuration of said second openend.
 4. A jet nozzle for use in a micronizing jet mill comprising: anozzle body having a first open end and a second open end, said firstand second ends being joined by a passageway passing through saidnozzle, wherein said second open end has a slot-like configurationdefined by two longer, essentially inwardly hyperbolic sides andopposing generally rounded ends; a coanda effect inducing elementpositioned within said passageway, said coanda effect inducing elementextending outward from said nozzle through said second end, wherein saidcoanda effect inducing element has a configuration substantially similarto the slot-like configuration of said second open end.
 5. A jet nozzlefor use in a micronizing jet mill comprising: a nozzle body having afirst open end and a second open end, said first and second ends beingjoined by a passageway passing through said nozzle, wherein said secondopen end has a slot-like configuration defined by two longer,essentially inwardly hyperbolic sides and opposing generally roundedends; a coanda effect inducing element positioned within saidpassageway, said coanda effect inducing element extending outward fromsaid nozzle through said second end, wherein said coanda effect inducingelement has a configuration substantially similar to the slot-likeconfiguration of said second open end, said coanda effect inducingelement extends outwardly from said second open end of about 2.5 mm toabout 38.1 mm.
 6. A jet nozzle for use in a micronizing jet millcomprising: a nozzle body having a first open end and a second open end,said first and second ends being joined by a passageway passing throughsaid nozzle, wherein said second open end has a slot-like configurationdefined by two longer, essentially inwardly hyperbolic sides andopposing generally rounded ends; a coanda effect inducing elementpositioned within said passageway, wherein the exterior surface of saidcoanda effect inducing element and the interior surface of saidslot-like opening define a gap, said coanda effect inducing elementextending outward from said nozzle through said second end, wherein saidcoanda effect inducing element has a configuration substantially similarto the slot-like configuration of said second open end and wherein theportion of said coanda effect inducing element which conforms to theconfiguration of said second open end extends into said passageway adistance ranging from about ten times said gap to about 20 times saidgap.
 7. A jet nozzle for use in a micronizing jet mill comprising: anozzle body having a first open end carrying interior threads and asecond open end having a slot-like opening, said first and second endsbeing joined by a passageway passing through said nozzle; a coandaeffect inducing element positioned within said passageway and extendingoutward from said nozzle through said second end, wherein said coandaeffect inducing element has an external geometric configurationsubstantially conforming to the internal configuration of said slot-likeopening of said second end of said nozzle body and wherein the exteriorsurface of said coanda effect inducing element and the interior surfaceof said slot define an air passage; and, a coanda effect inducingelement retainer positioned within the first end of said nozzle, therebysecuring said coanda effect inducing element within said passageway. 8.A jet nozzle for use in a micronizing jet mill comprising: a nozzle bodyhaving a first open end carrying interior threads and a second open endhaving a slot-like opening, said first and second ends being joined by apassageway passing through said nozzle; a coanda effect inducing elementpositioned within said passageway and extending outward from said nozzlethrough said second end, wherein said coanda effect inducing element hasan external geometric configuration substantially conforming to theinternal configuration of said slot-like opening of said second end ofsaid nozzle and wherein the exterior surface of said coanda effectinducing element and the interior surface of said slot-like openingdefine a gap; and, a coanda effect inducing element retainer positionedwithin the first end of said nozzle, wherein said retainer has apassageway passing therethrough, thereby securing said coanda effectinducing element within said passageway.
 9. A jet nozzle for use in amicronizing jet mill comprising: a nozzle body having a first open endand a second open end, said first and second ends being joined by apassageway passing through said nozzle, wherein said second open end hasa slot-like configuration; a coanda effect inducing element adjustablypositioned within said passageway, said coanda effect inducing elementextending outward from said nozzle through said second end, wherein saidcoanda effect inducing element has a configuration substantially similarto the slot-like configuration of said second open end.
 10. A jet nozzlefor use in a micronizing jet mill comprising: a nozzle body having afirst open end and a second open end, said first and second ends beingjoined by a passageway passing through said nozzle, wherein said secondopen end has a slot-like configuration; a coanda effect inducing elementpositioned within said passageway, wherein the exterior surface of saidcoanda effect inducing element and the interior surface of saidslot-like opening define a gap; said coanda effect inducing elementextending outward from said nozzle through said second open end about2.5 mm to about 38.1 mm, wherein said coanda effect inducing element hasa configuration substantially similar to the slot-like configuration ofsaid second open end and wherein the portion of said coanda effectinducing element which conforms to the configuration of said second openend extends into said passageway a distance ranging from about ten timessaid gap to about 20 times said gap.
 11. A jet nozzle for use in amicronizing jet mill comprising: a nozzle body having a first open endand a second open end, said first and second ends being joined by apassageway passing through said nozzle, wherein said second open end hasa slot-like configuration defined by two longer, essentially inwardlyhyperbolic sides and opposing generally rounded ends; a coanda effectinducing element positioned within said passageway, wherein the exteriorsurface of said coanda effect inducing element and the interior surfaceof said slot-like opening define a gap; said coanda effect inducingelement extending outward from said nozzle through said second open endabout 2.5 mm to about 38.1 mm, wherein said coanda effect inducingelement has a configuration substantially similar to the slot-likeconfiguration of said second open end and wherein the portion of saidcoanda effect inducing element which conforms to the configuration ofsaid second open end extends into said passageway a distance rangingfrom about ten times said gap to about 20 times said gap.